The disclosure relates generally to the distribution of electrical power, audio signals, and control signals in audio systems used in applications collectively referred to as sound reinforcement. In particular, the disclosure relates to the distribution of electrical power, audio signals, and control signals in audio systems that utilize power amplifiers, signal processing equipment and audio networking components.
Large arrays of loudspeaker enclosure assemblies have been standard for producing high sound pressure levels for concert production and performance installation for several decades. Since these assemblies are then joined together to form an array of the desired geometry, functionality and performance, the more sophisticated loudspeaker enclosure assemblies are now frequently called array elements that, when assembled in a group for use, are referred to as a loudspeaker array. In nearly all applications in large venues arrays are raised above the audience with electric chain hoists utilizing rigging hardware attached to the array element. This process is referred to as “flying” a sound system. Once an array is in the air, it is said to be “flown”.
Loudspeaker arrays have for many decades been provided an amplified signal from power amplifiers in equipment racks, which are located at floor level behind an array if the array is stacked on the ground, or are located beneath an array if it is raised into the air with rigging equipment (flown). In some cases the amplifier racks may be elevated with a flown array or placed, for example on an elevated catwalk in a stadium. In a large concert, each array may require mains power in the range of 20-50 kilowatts. Large systems are most frequently powered by a 220-230 volt three-phase supply.
Racks of amplifiers are typically provided a conditioned audio signal specific to the requirement of the audio transducers within the array elements that the amplifiers are powering. Typical audio signals are either analog or digital.
In more complex examples, power amplifiers are devised with a variety of audio and control inputs. Network endpoints, digital audio and analog inputs are common for delivery of the audio signal while the control may be delivered via a dedicated serial line, Ethernet or other IP transport. DSP is commonly added to such amplifiers and is found physically within the amplifier and electrically prior to its input stage. Amplifiers such as these can be referred to as networked processed amplifiers.
In the last decade, it has become common practice in small professional use loudspeaker systems to place one or more channels of power amplification within the loudspeaker system and provide connections to supply electrical power to the amplifier and an audio signal to the amplifier. This allows the manufacturer to define and control a closely matched relationship between the transducers and the amplifiers. In such systems, the signal sent to the loudspeaker is generally processed in a user programmable DSP prior to its delivery to the powered loudspeaker. The program in the DSP would be configured to divide the signal spectrally and further equalize it to achieve the desired response from the loudspeaker. Optimization of both cost and performance can therefore be maximized. Such loudspeakers are referred to as powered loudspeakers. A limitation exists however with this structure since the operator may configure the DSP incorrectly for the loudspeaker.
Somewhat more complex loudspeaker designs incorporate DSP into the loudspeaker enclosure assembly. This step insures that the operator of the system always maintains a correct match between the transducers, power and DSP. Loudspeakers such as these can be referred to as powered and processed loudspeakers.
In more advanced systems, the signal is transmitted to the loudspeaker system via network audio. This configuration allows for more creative control of sound system architecture as well as adding an element of user friendliness. Notwithstanding their complexity, small systems such as these do not generally create insurmountable operational problems since small loudspeakers are most often employed where they are accessible by a technician.
Powered array elements for use in the largest audio systems have been available for more than a decade. An assembly of powered array elements is often referred to as a powered array. The first of these systems in the market employed simple electrical powering and audio signal connection schemes. Typically a rubber coated cable (cab tire) with locking plugs and sockets is used to energize the amplifiers with mains voltage. The audio signal is fed to the array elements via a separate shielded cable.
In more recent examples now in use, the power and signal are first fed into a compact rack mounted module. There they are combined into a single multi-pin connector and then passed to the powered array element through a multi conductor cable which is designed to carry both signal and electrical power.
In most cases, additional signal transceivers are required, for transmitting system control data or information gathered from the powered array element. In examples where the audio signal is AES/EBU transmitted on a twisted pair of conductors, additional conductors may be required. In examples where networked audio is used, all the required information can be exchanged via the network.
Unfortunately, in spite of the benefit of integrating system components, powered arrays have proven to be operationally difficult and susceptible to problems associated with the interruption of audio signals. The interruption of audio signals in such systems occurs at a significant cost. Highly paid entertainers performing in front of large audiences, heads of state addressing nations and religious leaders addressing hundreds of thousands of followers illustrate the penalty for audio system failure.
The interruption of audio signals in powered array systems can result, for example, from loss of control of the power amplifiers, loss of control of DSP system, and/or loss of audio network signal. When these problems occur, they are exacerbated by the poor accessibility of the electronics, since most systems are flown in use.
A particular problem associated with loss of power and/or signal or control transmission is the time required for electrical components within the powered array element to recover. The recovery time of electrically energized audio components following a power failure varies widely. Typically, older analog components will restart with the least time delay. Digital audio devices generally take longer to recover since most devices contain a CPU or microcontroller of some sort that must reboot its software or firmware before it is ready for use.
Audio network devices are the most prone to delay upon restart since the device must first reboot its internal software and then reconnect to other devices on the network. In some cases, significant additional delays may be encountered because of lost network configuration information. For example, network connections and configurations may involve excessive time to restore after power failures that were accompanied by erratic electrical interference. Some delays can extrapolate into a network crash that can demand hours of debugging time from system engineers.
In light of these issues with powered array elements, some users take steps such as running parallel analog lines and/or network lines for redundancy purposes. Specifically, the stability of network audio signals is subject to some of the same limitations as Ethernet based networks such as sensitivity to electrical power fluctuations.
These problems can occur due to a host of causes, such as exposure of the array element and electronics to adverse weather conditions, which can interfere with electrical performance. Other limitations of powered array elements include the complexity of the design process, the increased weight of the array element, and presently, the lack of an industry standard.
Powered arrays do not presently adhere to an industry standard, although acceptance of the concept is becoming more widespread. Some manufacturers, on the other hand, have stated emphatically that they will not participate in the development of any powered array elements. One reason of the slow acceptance of this technology is the lack of a universally accepted network audio standard. The result is a host of proprietary hardware solutions, of which many lack the sophistication which results from standardization and mass production. Another aspect is the perception that the electronic technology within the array element will be difficult to control in any failure mode and inaccessible for service, as described above.
It is further noted that that while these problems are most apparent in the powered and processed array, conventionally powered loudspeakers which are networked in an array can be susceptible to similar problems. Even though the amplifiers and network electronics are more accessible, power fluctuations and interruptions can equally interfere with network and audio signal integrity.
Some system users have attempted to provide backup power to a loudspeaker array using an uninterruptable power supply (UPS). UPS battery voltages typically range from 12 to 72 VDC. In a small UPS, the battery may be a single unit at the lower end of the voltage range, whereas in large UPSs, the batteries will include multiple units generally connected in a series parallel circuit. Typically, a UPS providing inverter output of 240 volts will have a battery voltage not exceeding 72 VDC.
Inverter output voltage and power will generally vary according to requirement. A small UPS for a personal computer in North America will have an output voltage of 115 volts and a capacity of several hundred watts. A large industrial UPS might have a three phase output of up to 600 volts and capacities in excess of 50 kilowatts
In order to provide backup power to a loudspeaker system, a UPS would be required to supply the full power to the amplifiers that power the array. A typical single high powered array element would require a UPS capable of supplying input electrical power in the order of 2-3 kilowatts; a large array of such elements will require input power in excess of 50 kilowatts. An array will be typically powered by a three phase supply at 220-240 volts. The same calculation applies to powered arrays as well as conventional arrays.
A typical UPS of that size would occupy nearly one cubic meter of space, weigh somewhat more than a tone and dissipate more than 15,000 BTUs during operation. Furthermore, available UPSs are designed assuming the presence of standby generator power. Typical battery life is less than five minutes. An UPS of this size and configuration, in most applications, is therefore not a practical solution for an audio system.